'Singing frog' communicates via squeaks

A frog that sings like a bird has been found to possess another unusual trait - it can communicate in high-pitch squeaks that are inaudible to the human ear.

The frog lives in the fast-moving streams and waterfalls of east-central China and uses ultrasonic calls to make itself heard above the loud background noise of running water.

It is the first time that an animal other than bats, marine mammals and some rodents has been found to be capable of producing and hearing high-frequency ultrasound.

Scientists discovered some years ago that the concave-eared torrent frog emits ultrasounds but the latest study published in the journal Nature shows that the sounds are used as calls rather than being simply a by-product of other vocalisations.

The human ear cannot hear sounds with frequencies higher than 20 kilohertz but the frog has been recorded emitting sounds higher than 128 kilohertz which can carry above the noise of splashing water.

"Nature has a way of evolving mechanisms to facilitate communication in very adverse situations," said Professor Albert Feng of the University of Illinois at Urbana-Champaign.

"One of the ways is to shift the frequencies beyond the spectrum of the background noise.

Mammals such as bats, whales and dolphins do this, and use ultrasound for their sonar system and communication," he said.

The frog - Amolops tormotus - has an unusually recessed ear canal which protects a thin and delicate eardrum that can detect high-frequency sounds, Professor Feng said.

"Thin eardrums are needed for detection of ultrasound.

Recessed ears shorten the path between eardrums and the ear, enabling the transmission of ultrasound to the ears," he said.

Scientists recorded fragments of the high-frequency calls and found that other frogs responded to the recordings by making their own calls in return.

"Humans have always been fascinated by how some animals can discern their world through a sensing system vastly different from our own," Professor Feng said.

"That frogs can communicate with ultrasound adds to that list and represents a novel finding because we normally think such ability is limited to animals equipped with a sophisticated sonar system," he said.

"This suggests that there are likely many other examples of unexpected forms of communication out there."

Understanding the nature of ultrasonic communication in frogs could help scientists to understand human hearing and deafness, said James Battey, director of the US National Institute for Deafness.

"In the study of communication and communication disorders, researchers can gain a great deal of insight by looking at the natural world," Dr Battey said.

"The more we can learn about the extraordinary mechanisms that this frog and other animals have developed to hear and communicate with one another, the more fully we can understand the hearing process in humans, and the more inspired we can be in developing new treatments for hearing loss," he said.

- INDEPENDENT